Page 163 - DCAP311_DCAP607_WIRELESS_NETWORKS

Unit 10: Wireless MAN Technologies

(c) IEEE 802.11i/WPA2: Notes
The IEEE is finalized the 802.11i standard, which is based on a far more robust
encryption technique called the Advanced Encryption Standard. The Wi-Fi Alliance
designate products that comply with the 802.11i standard as WPA2.
However, implementing 802.11i requires a hardware upgrade.

The picture has become somewhat confused as service providers started using Wi-Fi
to deliver services for which it was not originally designed. The two major examples
of this are wireless ISPs and city-wide Wi-Fi mesh networks.
(d) Wireless ISPs (WISPs):
One business that grew out of Wi-Fi was the Wireless ISP (WISP). This is the idea
of selling an Internet access service using wireless LAN technology and a shared
Internet connection in a public location designated a hot spot.
From a technical standpoint, access to the service is limited based on the transmission
range of the WLAN technology. You have to be in the hot spot (i.e. within 100m of
the access point) to use it. From a business standpoint, users either subscribe to a
particular carrier.s service for a monthly fee or access the service on a demand basis
at a fee per hour. While the monthly fee basis is most cost effective, there are few
intercarrier access arrangements so you have to be in a hot spot operated by your
carrier in order to access your service.
(e) City-Wide Mesh Networks:
To address the limited range, vendors like Mesh Networks and Tropos Networks
have developed mesh network capabilities using Wi-Fi’s radio technology.
The idea of a radio mesh network is that messages can be relayed through a number
of access points to a central network control station. These networks can typically
support mobility as connections are handed off from access point to access point as
the mobile station moves.

Some municipalities are using Wi-Fi mesh networks to support public safety
applications (i.e. terminals in police cruisers) and to provide Internet access to the
community (i.e. the city-wide hot spot).
WiFi systems use two primary radio transmission techniques.
802.11b (<=11 Mbps): The 802.11b radio link uses a direct sequence spread spectrum technique
called complementary coded keying (CCK). The bit stream is processed with a special coding and
then modulated using Quadrature Phase Shift Keying (QPSK).
802.11a and g (<=54 Mbps): The 802.11a and g systems use 64-channel orthogonal frequency
division multiplexing (OFDM). In an OFDM modulation system, the available radio band is
divided into a number of sub-channels, and some of the bits are sent on each. The transmitter
encodes the bit streams on the 64 subcarriers using Binary Phase Shift Keying (BPSK), Quadrature
Phase Shift Keying (QPSK), or one of two levels of Quadrature Amplitude Modulation (16, or 64-
QAM). Some of the transmitted information is redundant, so the receiver does not have to receive
all of the sub-carriers to reconstruct the information.

Did u know? The original 802.11 specifications also included an option for frequency
hopping spread spectrum (FHSS), but that has largely been abandoned.

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